A Prescription for Trouble

ANSWER
The correct interpretation includes normal sinus rhythm, right atrial enlargement, left ventricular hypertrophy, and a prolonged QT interval. Normal sinus rhythm is indicated by a P for every QRS and a QRS for every P, with a constant PR interval (see rhythm strip of lead I).

Right atrial enlargement is evidenced by the tall P waves in leads II, III, aVF, and V₁. Note that there is no biphasic P wave in lead V₁, so there is no evidence of accompanying left atrial enlargement.

High-voltage limb leads (sum of R in lead I and S in lead III ≥ 25 mm) or precordial leads (sum of S in V1 and R in V₅ or V₆ ≥ 35 mm) are indicative of left ventricular hypertrophy.

The QTc interval of 653 ms with a normal sinus rate is worrisome for prolonged QT syndrome. A review of the history shows the patient to be taking two drugs (lithium, azithromycin) known to prolong the QT interval. Although it is not known whether this patient has inherent QT prolongation, use of these types of agents should be avoided.